In electronic systems, input signals are processed through various components before they are available as an output signal as desired. Due to various imperfections of electronic components, harmonics of the input signal are generated at the output. Harmonics are manifested in output currents and voltages at integer multiples of the fundamental frequency of the input signal. Harmonics can cause signal distortions and can lead to malfunctioning of electronic systems resulting in downtime and increased operating costs. In communication systems especially wireless communication systems, harmonics can distort data resulting in incorrect data interpretation.
To eliminate harmonics, various harmonic filtering techniques are used to filter out undesired harmonics and generate clean signal. Typically, harmonic filters are added towards the end of the circuit to capture or ‘trap’ harmonics and filter undesired output signal at multiples of the fundamental frequency. These filters add extra cost for manufacturing of electronic systems and for high volume manufacturing, harmonic filters become cost prohibitive.
In wireless communication, to communicate over long distance using a communication device such as a cellular phone, high output power amplifiers are needed; however, to comply with FCC regulations, strong out-of-band filtering is employed using external components in the communication devices for impedance conversion. Traditional solutions realize high efficiency transmitters by driving transmitters near rail waveforms and use many external components to filter out harmonics of the fundamental tone. This solution typically requires a high voltage transistor to sustain high waveform swing and many externals components to filter out harmonics which increases the losses. These external components are highly undesirable in the communication device because they add cost and use up significant battery power. Ideally, electronic systems need to be designed such to avoid undesired harmonics in the output signal and reduce the cost of products.